This patent deals generally with batteries and more specifically with an emitter for a thermophoto electric generator.
Thermophotovoltaic cells are used to convert thermal energy into electrical energy by heating an emitter to a temperature at which it becomes incandescent and directing the radiation from the incandescent emitter to a photovoltaic cell. Although the energy conversion actually can take place with very simple devices, even as simple as a candle and a photocell, the practical use of such systems depends upon increasing the efficiency of the energy conversion. Very few devices are presently available which have efficiencies high enough to make them suitable for use in generating usable electrical energy.
Essentially, the problem is that most heated materials emit radiation over a very broad spectrum, and that photovoltaic cells have a very narrow band of sensitivity. Although selective filters have been used to limit the band of radiation to which the photovoltaic cell is subjected, these filters are very fragile and require flame shields when used with flame fired systems. Ideally, a selective radiator is needed which only emits radiation in the same narrow band to which the photovoltaic cell responds.
It is already known that certain rare earth oxides emit radiation in a single narrow band in the infrared spectrum when they are heated. These oxides of the rare earth elements, such as erbium, holmium, neodymium, and ytterbium, exhibit peak radiation in a narrow band, and their emittance approaches zero elsewhere, and, fortunately, their band of emission closely matches the band of sensitivity of photovoltaic cells.
However, there is considerable difficulty in heating rare earth oxides in practical devices. The heating process always involves also heating other materials in order to transfer the heat to the rare earth oxides, and these other materials and the bonds to the other materials have experienced mechanical failures due to thermal stress.